When extra-heavy oils or bitumen are extracted from oil sand or oil shale reservoirs using piping systems, it is necessary to achieve the greatest possible flowability of the oils to be extracted. The piping systems are introduced here through bore holes provided for this purpose. For instance, an increase in the flow speed can be achieved by increasing the temperature of the reservoirs (underground reservoirs). According to the prior art, induction heaters, known as inductors, are used herefor. Inductive heating is used exclusively or in an assistive manner to increase the temperature particularly with a steam-assisted gravity drainage method (SAGD method).
In order to achieve a heating output which is adequate for the required increase in temperature, large current intensities of a few hundred amperes are typically required, since the reservoir surrounding the inductor is in most cases only slightly electrically conductive. Moreover, an alternating current intensity is applied to the inductor, the frequency of which typically lies in the range of 10 kHz to 200 kHz. As a result, a high inductive voltage drop along an elongated inductor is however produced, the length of which can in most instances amount to more than 1 km. In most cases the inductive voltage drop therefore lies in the order of magnitude of a few 100 kV. Such a voltage can, in practice, only be handled easily, thereby rendering it necessary to compensate for this.
Such a compensation can take place for instance by capacitors connected in series, as described in the patent specification DE: 10 2007 040 605.5. The current-carrying conductors of the inductor are interrupted here and as a result have interruption locations.
The disadvantage of such a series connection of capacitors is that the interruptions embody weak points of the inductor. Partial discharges may occur at the interruption locations which may result in damage to the inductor.